Astronomy:Sigma Coronae Borealis

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Short description: Star in the constellation Corona Borealis
Not to be confused with S Coronae Borealis.
Sigma Coronae Borealis
Location of σ Coronae Borealis (circled)
Observation data
{{#ifeq:J2000|J2000.0 (ICRS)|Epoch J2000.0      Equinox J2000.0 (ICRS)| [[History:Epoch|Epoch J2000]]      [[Astronomy:Equinox (celestial coordinates)|Equinox J2000}}
Constellation Corona Borealis
σ CrB A (σ2)
Right ascension  16h 14m 40.853s[1]
Declination +33° 51′ 31.01″[1]
Apparent magnitude (V) 5.55[2]
σ CrB B (σ1)
Right ascension  16h 14m 40.387s[3]
Declination +33° 51′ 27.10″[3]
Apparent magnitude (V) 6.419[2]
σ CrB C
Right ascension  16h 13m 56.268s[4]
Declination +33° 46′ 24.10″[4]
Apparent magnitude (V) 12.229[5]
Characteristics
σ CrB
Spectral type F6V (A)[6] + G1V (B)[7]
U−B color index +0.045[8]
B−V color index +0.599[8]
Variable type RS CVn[9]
σ CrB C
Spectral type M2.5V[10]
Astrometry
σ CrB A
Radial velocity (Rv)−12.30±0.06[11] km/s
Proper motion (μ) RA: −268.216[1] mas/yr
Dec.: −87.282[1] mas/yr
Parallax (π)44.0575 ± 0.0459[1] mas
Distance74.03 ± 0.08 ly
(22.70 ± 0.02 pc)
Absolute magnitude (MV)+4.02[12]
σ CrB B
Radial velocity (Rv)−12.30±0.06[11] km/s
Proper motion (μ) RA: −290.860 mas/yr
Dec.: −78.524 mas/yr
Parallax (π)44.1340 ± 0.0179[3] mas
Distance73.90 ± 0.03 ly
(22.658 ± 0.009 pc)
Absolute magnitude (MV)+4.64[12]
σ CrB C
Radial velocity (Rv)−16.30±10[13] km/s
Proper motion (μ) RA: −286.965[4] mas/yr
Dec.: −89.818[4] mas/yr
Parallax (π)44.2674 ± 0.1586[4] mas
Distance73.7 ± 0.3 ly
(22.59 ± 0.08 pc)
Absolute magnitude (MV)+10.41[14]
Orbit[15]
Primaryσ2 CrB primary
Companionσ2 CrB secondary
Period (P)1.139791423(80) days
Semi-major axis (a)1.225±0.013 mas
Eccentricity (e)0.0
Inclination (i)28.08±0.34°
Longitude of the node (Ω)207.93±0.67°
Periastron epoch (T)2450127.61845(20)
Argument of periastron (ω)
(secondary)		0.0°
Orbit[15]
Primaryσ2 CrB
Companionσ1 CrB
Period (P)726±62 yr
Semi-major axis (a)5.26±0.35″
Eccentricity (e)0.72±0.01
Inclination (i)32.3±4.1°
Longitude of the node (Ω)28.0±0.5°
Periastron epoch (T)B 1825.2±1.5
Argument of periapsis (ω)
(primary)		237.3±6.8°
Orbit[16]
Primaryσ CrB Ca
Companionσ CrB Cb
Period (P)52 yr
Semi-major axis (a)0.111″
Eccentricity (e)0.36
Inclination (i)59°
Longitude of the node (Ω)30°
Periastron epoch (T)B 1963.0
Argument of periastron (ω)
(secondary)		127°
Details
σ2 CrB primary (Aa)
Mass1.137±0.037[15] M☉
Radius1.244±0.050[15] R☉
Surface gravity (log g)4.5[15] cgs
Temperature6,050±150[15] K
Metallicity [Fe/H]0.0[15] dex
Rotational velocity (v sin i)26±1[15] km/s
Age0.5 to 1.5[15] Gyr
σ2 CrB secondary (Ab)
Mass1.090±0.036[15] M☉
Radius1.244±0.050[15] R☉
Surface gravity (log g)4.5[15] cgs
Temperature5,870±150[15] K
Rotational velocity (v sin i)26±1[15] km/s
Age0.5 to 1.5[15] Gyr
σ1 CrB (B)
Mass1.0[15] M☉
Radius1.020±0.001[3] R☉
Surface gravity (log g)4.5[15] cgs
Temperature5,950±100[15] K
Rotational velocity (v sin i)3±2[15] km/s
Age1 to 3[15] Myr
σ CrB Ca
Mass0.423±0.042[17] M☉
Radius0.437±0.020[17] R☉
Surface gravity (log g)5.0[18] cgs
Temperature3,454±63[17] K
Metallicity [Fe/H]−0.06±0.03[17] dex
Age2.95[17] Gyr
Other designations
σ CrB, 17 CrB, BD+34°2750, GJ 605.2, SAO 65165, ADS 9979, CCDM J16147+3352, WDS J16147+3352[9]
σ CrB A: σ2 CrB, TZ CrB, GJ 9550A, HD 146361, HIP 79607A, HR 6063, TYC 2583-1846-1[19]
σ CrB B: σ1 CrB, GJ 9550B, HD 146362, HIP 79607B, HR 6064, TYC 2583-1846-2[20]
σ CrB C: GJ 9549, HIP 79551, G 180-42[21]
Database references
SIMBADσ CrB
σ1 CrB
σ2 CrB
σ CrB C
ARICNSσ1 CrB
σ2 CrB
σ CrB C

Sigma Coronae Borealis is a multiple star system in the northern constellation of Corona Borealis. Its name is a Bayer designation that is Latinized from σ Coronae Borealis and abbreviated Sigma CrB or σ CrB. This is a quintuple star system containing three sunlike main-sequence stars and two other low-mass stars. The combined visual magnitude is 5.3 and the system lies 74 light years from Earth. σ CrB A is the variable star TZ Coronae Borealis.

System components

Aa
Period = 1.14 d
Ab
Period = 726 yr
B (σ1)
Period = 877,000 yr
Ca
Period = 52 yr
Cb

Hierarchy of orbits[22]

The brightest components of Sigma Coronae Borealis form a visual binary with an angular separation of 7 arcsecond first resolved in the 19th century,[23] and are designated σ Corona Borealis A and B. More recently, the designations σ2 and σ1 Corona Borealis have come into use. Somewhat confusingly, the brighter component A is referred to as σ2 because it has the higher right ascension. A third component, while being separated by 635″ (translating to a minimum distance of 14,000 au), has a similar parallax and proper motion to the brighter stars and is physically associated. It is known in the Washington Double Star Catalog (WDS), a compilation of observations of double stars, as component E,[23] but it is usually called Sigma Coronae Borealis C.[15]

Sigma1 Corona Borealis is a G-type main-sequence star like the Sun, and has similar parameters: a mass roughly equal to that of the Sun, and an effective temperature of 5950 K.[15] A visual orbit has been calculated, with a period of about 730 years and a high eccentricity of 0.72.[15]

Sigma2 Corona Borealis itself is a close binary. Here, the two stars are extremely close and orbit fairly quickly, every 1.14 days.[15] This tiny separation of only 0.0279 au[15] has allowed the two stars to exert tidal forces on each other, leading to synchronization of their rotation. They have also been classified as RS Canum Venaticorum variables (RS CVn)—young, active stars that show variability in their apparent magnitude due to starspots on their surfaces.[9]

Despite Sigma2 Corona Borealis's two stars being separated only by about the diameter of each star, they were resolved using the CHARA optical interferometer at the Mount Wilson Observatory. As of 2006, it is the shortest-period binary ever to be resolved. The primary is 13.7% more massive than the Sun, while the secondary is 9.0% more massive than the Sun, and both are 24.4% wider than the Sun.[15]

σ Coronae Borealis C, also known as HIP 79551, appears as a red dwarf with a spectral type of M2.5V.[10] It too is a binary star, with a companion in a 52-year orbit. The companion has a mass of 0.10 M☉ and has been detected through astrometry.[16][15]

Optical companions

The Washington Double Star Catalog (WDS), a compilation of observations of double stars, lists several components to the main system. Two of those are listed in the WDS as components C, and D. As of 1984, component C was separated from the primary by 18″ along a position angle of 103° and as of 1996, component D was separated from the primary by 88″ along a position angle of 82°. However, both of them have different proper motions through space and are not related, just optical alignments.[23]

Variability

A light curve for TZ Coronae Borealis, plotted from TESS data[24]

The spectroscopic binary σ2 CrB is an RS Canum Venaticorum variable. It varies in brightness by 0.05 magnitudes every 1.139789 days, the same as the orbital period. The brightness changes are caused by variations in surface brightness on the stars, effectively giant sunspots. Variable star designations are not given to stars with Bayer designations, but in this case only one component of σ Coronae Borealis is identified as variable, so it has the designation TZ Coronae Borealis.[25]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 Høg, E. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics 355: L27–L30. Bibcode: 2000A&A...355L..27H. 
  3. ↑ 3.0 3.1 3.2 3.3 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  4. ↑ 4.0 4.1 4.2 4.3 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  5. ↑ Zacharias, N. (2012). "The fourth US Naval Observatory CCD Astrograph Catalog (UCAC4)". VizieR On-line Data Catalog 1322. Bibcode: 2012yCat.1322....0Z. 
  6. ↑ Strassmeier, K. G. (1994). "Chromospheric activity in G and K giants: the spectroscopic data base". Astronomy and Astrophysics Supplement 103 (103): 413–425. Bibcode: 1994A&AS..103..413S. 
  7. ↑ Gray, R. O. et al. (2003). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I". The Astronomical Journal 126 (4): 2048. doi:10.1086/378365. Bibcode: 2003AJ....126.2048G. 
  8. ↑ 8.0 8.1 Rakos, K. D. et al. (1982). "Photometric and astrometric observations of close visual binaries". Astronomy and Astrophysics Supplement Series 47 (221–235): 221. Bibcode: 1982A&AS...47..221R. 
  9. ↑ 9.0 9.1 9.2 "* sig CrB". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=%2A+sig+CrB. 
  10. ↑ 10.0 10.1 Reid, I. Neill et al. (1995). "The Palomar/MSU Nearby-Star Spectroscopic Survey. I. The Northern M Dwarfs -Bandstrengths and Kinematics". The Astronomical Journal 110: 1838. doi:10.1086/117655. Bibcode: 1995AJ....110.1838R. 
  11. ↑ 11.0 11.1 Karataș, Yüksel et al. (2004). "Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution". Monthly Notices of the Royal Astronomical Society 349 (3): 1069–1092. doi:10.1111/j.1365-2966.2004.07588.x. Bibcode: 2004MNRAS.349.1069K. 
  12. ↑ 12.0 12.1 Boro Saikia, S. et al. (2018). "Chromospheric activity catalogue of 4454 cool stars. Questioning the active branch of stellar activity cycles". Astronomy and Astrophysics 616. doi:10.1051/0004-6361/201629518. Bibcode: 2018A&A...616A.108B. 
  13. ↑ Hawley, Suzanne L. et al. (1996). "The Palomar/MSU Nearby Star Spectroscopic Survey.II.The Southern M Dwarfs and Investigation of Magnetic Activity". The Astronomical Journal 112: 2799. doi:10.1086/118222. Bibcode: 1996AJ....112.2799H. 
  14. ↑ Houdebine, Éric R. et al. (2019). "The Mass-Activity Relationships in M and K Dwarfs. I. Stellar Parameters of Our Sample of M and K Dwarfs". The Astronomical Journal 158 (2): 56. doi:10.3847/1538-3881/ab23fe. Bibcode: 2019AJ....158...56H. 
  15. ↑ 15.00 15.01 15.02 15.03 15.04 15.05 15.06 15.07 15.08 15.09 15.10 15.11 15.12 15.13 15.14 15.15 15.16 15.17 15.18 15.19 15.20 15.21 15.22 15.23 15.24 15.25 15.26 Raghavan, Deepak et al. (2009). "The Visual Orbit of the 1.1-day Spectroscopic Binary σ2 Coronae Borealis from Interferometry at the CHARA Array". The Astrophysical Journal 690 (1): 394–406. doi:10.1088/0004-637X/690/1/394. Bibcode: 2009ApJ...690..394R. 
  16. ↑ 16.0 16.1 Heintz, W. D. (1990). "Photographic astrometry of binary and proper-motion stars". The Astronomical Journal 99: 420. doi:10.1086/115340. Bibcode: 1990AJ.....99..420H. 
  17. ↑ 17.0 17.1 17.2 17.3 17.4 Mann, Andrew W. et al. (2015). "How to Constrain Your M Dwarf: Measuring Effective Temperature, Bolometric Luminosity, Mass, and Radius". The Astrophysical Journal 804 (1): 38. doi:10.1088/0004-637X/804/1/64. Bibcode: 2015ApJ...804...64M. 
  18. ↑ Lépine, S. (2013). "A Spectroscopic Catalog of the Brightest (J < 9) M Dwarfs in the Northern Sky". The Astronomical Journal 145 (4): 102. doi:10.1088/0004-6256/145/4/102. Bibcode: 2013AJ....145..102L. 
  19. ↑ "* sig02 CrB". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=%2A+sig02+CrB. 
  20. ↑ "* sig01 CrB". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=%2A+sig01+CrB. 
  21. ↑ "* sig CrB C". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=%2A+sig+CrB+C. 
  22. ↑ Tokovinin, Andrei (2018). "The Updated Multiple Star Catalog". The Astrophysical Journal Supplement Series 235 (1): 6. doi:10.3847/1538-4365/aaa1a5. Bibcode: 2018ApJS..235....6T. 
  23. ↑ 23.0 23.1 23.2 Mason, Brian D. et al. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal 122 (6): 3466. doi:10.1086/323920. Bibcode: 2001AJ....122.3466M. 
  24. ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html. 
  25. ↑ Kholopov, P. N. et al. (1981). "65th Name-List of Variable Stars". Information Bulletin on Variable Stars 1921: 1. Bibcode: 1981IBVS.1921....1K. 



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